Novel MOF(Zr)-on-MOF(Ce) adsorbent for elimination of excess fluoride from aqueous solution

Machine Learning Reveals Key Adsorption Mechanisms for Oxyanions Based on Combination of Experimental and Published Literature Data

The development of new adsorbents for water treatment often involves complex adsorption mechanisms, whose individual contributions are unclear, thereby limiting the understanding of adsorption driving forces, making it difficult to achieve precise design of adsorbents. Machine learning (ML) has been used to uncover the impacts of these mechanisms through feature engineering, but progress is limited by the data quality for training. Herein, we developed a universal ML strategy for precisely predicting the adsorption capacity of polymers for oxyanions and identifying the adsorption driving force based on the combination of experimental and published literature data. The adsorption mechanism was explored through classification of RDkit descriptors with different SHAP importance values, and electrostatic interaction was found to be the driving force in the oxyanion adsorption process, which was further verified by theoretical calculations, adsorption experiments, and effective targeted adsorbent design. In comparison, analysis relying on a separate literature data source led to decreased model performance, some biased conclusions, and invalid targeted adsorbent design. Overall, this study proposed a strategy for data set optimization as well as dominant mechanism identification, which could shed light on better treatment of oxyanions in wastewater.

In-situ anchoring of ZIF-8 nanoparticles on sodium alginate aerogel for efficient and rapid phenol adsorption from wastewater

The deep purification of highly toxic phenol in wastewater is a water purification issue of concern. Metal-organic frameworks (MOFs) have been widely used in the field of adsorption and separation owing to their advantages of high porosity and abundant active sites. However, powdered MOFs are easy to agglomerate and difficult to separate, which poses a great challenge to their adsorption performance and recycling, severely limiting their practical applications. To overcome these difficulties, an in situ nucleation and growth of ZIF-8 nanoparticles on sodium alginate aerogel was proposed to achieve efficient phenol adsorption. The introduction of ZIF-8 increases the number of adsorption sites. 3D aerogel structure effectively prevents ZIF-8 from agglomerating and increases the specific surface area to facilitate the exposure of active sites. This composite structure balances the utility and the powder nature of ZIF-8. Benefiting from the synergistic effect of advantageous structure, ZIF-8@SA-AG exhibits high adsorption capacity (91.5 mg g-1) within 60 min at an initial concentration of 70 mg L-1, which outperforms most of the reported phenol adsorbents under the similar conditions. This study provides a feasible solution for custom processing of MOFs powder and construction of diversified composite macro bulk adsorbents.

Cysteine-Functionalized Magnetic Manganese-Based MOF Composite for Enhanced Removal of Pb2+ from Water

Among the multitude of toxic water pollutants, Pb2+ poses a significant threat to human health. A novel magnetic manganese-based metal-organic framework (Mn-MOF) composite, MFCys, was designed for the selective removal of Pb2+. MFCys was readily synthesized through the postsynthetic modification of magnetic Mn-MOF/Fe3O4 (MF) with l-cysteine (l-Cys), utilizing a prospective Mn-MOF, {[Mn2(tzpa)(OH)(H2O)2]·DMA}n. MFCys demonstrated superior adsorption of Pb2+, reaching equilibrium within 2 h compared to Mn-MOF and MF. The Langmuir model indicated that MFCys underwent chemisorption of Pb2+. Meanwhile, the adsorption process aligned with the pseudo-second-order (PSO) kinetic model, confirming that Pb2+ was adsorbed by MFCys mainly through monolayer chemisorption. Thermodynamic results revealed that the adsorption of Pb2+ by MFCys was spontaneous and endothermic. Moreover, even in the presence of competing Cd2+, Zn2+, Ca2+, Mg2+, Na+, K+, and Pb2+, MFCys exhibited exceptional selectivity for Pb2+ due to the electrostatic interaction and the electronic coupling effect between MFCys and Pb2+. The magnetic MFCys enabled easy separation from the suspension within 1 min by using an external magnet for recycling. MFCys retained 98.0% of the initial adsorption capacity for Pb2+ after five cycles, demonstrating excellent reusability. Notably, MFCys displayed exceptional adsorption of Pb2+ in simulated lead-acid battery wastewater, retaining 98.3% of its pristine adsorption capacity for Pb2+ even after five cycles. These findings suggest that an easily separated Mn-MOF composite has promising application prospects in Pb2+ wastewater treatment.

Development of in-situ MOF-modified ceramic filters for enhancing fluoride removal in water supply for remote communities

Ensuring the safe removal of fluoride from drinking water poses a significant challenge in numerous remote communities affected by fluoride contamination. Therefore, this study focuses on the in-situ growth of MOF-AlFu on ceramic filters (CFs), thereby synthesizing in-situ MOF-modified ceramic filters (IMCFs) for effective fluoride removal from drinking water in such communities. Initially, we conducted response surface optimization of the IMCF preparation process, followed by comprehensive characterization. Based on SEM, XRD, and FTIR analyses, it is confirmed that AlFu successfully grows on the surfaces and within the pores of CFs, forming layered structures that enhance the effective adsorption of fluoride on IMCFs. Besides, zeta potential and FTIR results indicated that electrostatic adsorption, ion exchange and hydrogen bonding are the primary mechanisms of fluoride adsorption on IMCFs, which is also confirmed by the adsorption kinetics. The results of adsorption isotherms show that the maximum adsorption of IMCFs is 9.51 mg/g. Within the pH range of 4-10, IMCFs reduced the fluoride concentration from 10 mg/L to below 1.2 mg/L. Furthermore, the IMCF retains over 75 % of its adsorption capacity after undergoing five use cycles, exhibiting remarkable durability during the multiple cycling filtration process. This study suggests that the developed IMCF can serve as a safe and effective defluoridation technology for purifying drinking water in remote communities.

Simultaneous adsorption and fluorescent sensing of ampicillin based on a trimetallic metal-organic framework

Antibiotic residue is a growing concern for human health, and exploring a method for antibiotic detection is imperative Herein, a trimetallic metal-organic framework (NH2-MIL-53(Al)@Mo/Zn-MOF) with an adsorption effect was prepared by growing Mo/Zn-MOF on the surface of NH2-MIL-53(Al) for simultaneous pre-concentration and detection of ampicillin (AMP). The NH2-MIL-53(Al)@Mo/Zn-MOF showed a large specific surface area and stable crystal structure, which is conducive to improving the adsorption efficiency and detection sensitivity. The adsorption process of NH2-MIL-53(Al)@Mo/Zn-MOF to AMP was simulated by a quasi-second-order kinetic model and Langmuir model. Moreover, a ratiometric fluorescent sensor was established based on fluorescence donors of NH2-MIL-53(Al)@Mo/Zn-MOF and CdTe QDs@SiO2 and a quencher of mitoxantrone (MIT). With the increasing concentration of AMP, the fluorescence of CdTe QDs@SiO2 was gradually quenched by MIT through the inner filter effect (IFE) and photoinduced electron transfer (PET) process. At the same time, that of NH2-MIL-53(Al)@Mo/Zn-MOF was maintained. With this strategy, the sensor achieved an ultra-sensitive detection of AMP with a low detection limit of 0.69 nM. Moreover, the constructed sensor exhibited satisfactory accuracy and reliability for AMP detection in food and environmental samples, which provides a new idea for developing integrated sensors for simultaneous adsorption and detection of antibiotics.

Enhanced fluoride removal from drinking water by activated carbon supported Ce-Al oxides: performance and mechanism

Elevated fluoride levels in drinking water pose a significant challenge to human health, necessitating affordable and effective adsorbents for fluoride removal. This study presents the synthesis of a Ce-Al binary metal oxide composite adsorbent supported on activated carbon (Ce-Al-O/AC) for the defluoridation of drinking water. The adsorbent, employing the synergistic bimetallic effect, demonstrates robust fluoride removal performance across a wide pH range of 4-10. It is worth highlighting that the equilibrium adsorption capacity reaches 17.97 mg g-1 at 298 K and pH 6 within 2 h, utilizing an adsorbent dose of 0.5 g L-1 in an initial 10 mg L-1 fluoride solution. The phosphate exerts the most significant influence on the defluoridation efficiency. The adsorption kinetics and isotherms align with the pseudo-second-order kinetics model and Langmuir isotherm model, respectively. Moreover, the defluoridation process is characterized as spontaneous and endothermic, with a maximum adsorption capacity of 31.65 mg g-1 at 298 K. Further experimental and theoretical evidences reveal that fluoride adsorption is primarily driven by electrostatic interactions and ion exchange. The dynamic adsorption tests coupled with economic analyses highlight the promise of Ce-Al-O/AC as a cost-effective and efficient adsorbent for practical drinking water defluoridation.

A porous metal-organic framework (Pd-MOF) as an efficient and recyclable catalyst for the C-O cross-coupling reactions

This report outlines the development of a novel and efficient metal-organic framework (MOF) synthesized through a hydrothermal reaction using palladium acetate salt and trimesic acid as the organic ligand. A series of detailed analyses, including FT-IR, XRD, EDS, TEM, XPS, BET, ICP, and SEM, were performed to characterize the resulting MOF. These analyses confirmed the successful integration of Pd within the metal-organic framework structure. Nitrogen adsorption-desorption analysis assessed the porosity of the Pd-T-MOF metal-organic framework. The specific surface area was measured at 206.3 m2/g based on isotherms. Using the BJH method, the total pore volume was calculated as 0.4 cm3/g, with an average pore diameter of 2.8 nm. The catalyst demonstrated exceptional catalytic performance and stability in facilitating the C-O cross-coupling reaction. The proposed protocol offers several advantages, such as catalyst reusability, mild reaction conditions, high product yields ranging from 58 to 98%, and short reaction times between 30 and 120 min. Furthermore, the adaptable nanocatalyst (Pd-T-MOF) can be easily separated from the reaction mixture via centrifugation and reused across four successive cycles with only a slight decrease in efficiency.

Multi-metal MOF-on-MOF metal-organic gel-based visual sensing platform for ultrasensitive detection of chlortetracycline and D-penicillamine

The widespread presence of antibiotic residues in the environment and food represents a significant threat to human health. In this study, a novel MOF-on-MOF (FCZE) gel with excellent peroxidase activity and strong fluorescence properties successfully synthesized by using Polyvinyl pyrrolidone (PVP) as a cross-linker and H₄BTEC as a ligand. Based on the energy transfer from the FCZE ligand to Eu luminescence, an ultrasensitive fluorescence method was developed for the detection of chlortetracycline (CTC), achieving a limit of detection (LOD) as low as 0.43 nM. Furthermore, the combination of FCZE with the 3,3',5,5'-tetramethylbenzidine (TMB)-hydrogen peroxide (H2O2) system enabled sensitive colorimetric detection of D-penicillamine (D-PA) with an LOD of 8.66 nM. Theoretical calculations reveal that the fluorescence quenching of FCZE by CTC is attributed to the inner filter effect of CTC and its suppression of the H4BTEC excited-state return to the ground state. Furthermore, Fukui function was employed for the first time to clarify the role of D-PA in scavenging free radicals and reducing oxidized TMB (oxTMB), providing a comprehensive understanding of the colorimetric detection mechanism. Additionally, a smartphone-assisted visual detection platform based on FCZE was developed for the detection of CTC and D-PA, with LODs of 0.71 μM and 0.13 μM, respectively. This study highlights the potential of nanomaterials for the simultaneous detection of multiple antibiotics, offering a novel strategy for the rapid and efficient monitoring of antibiotic residues in environmental samples.

Enhancing fluoride ion removal from aqueous solutions and glass manufacturing wastewater using modified orange peel biochar magnetic composite with MIL-53

In this study, we developed new adsorbents derived from orange peel biochar (BCOP) and enhanced them with CoFe2O4 magnetic nanoparticles (BCOP/CoFe2O4) and MIL-53(Al) (BCOP/CoFe2O4/MIL-53(Al)). These adsorbents were utilized to remove fluoride (FL) ions from aqueous solutions. We analyzed the properties of these adsorbents using a range of techniques, including FTIR, XRD, SEM, EDX-Map, VSM, Raman spectroscopy, and BET. Our findings indicate that the components interact effectively with one another. Specifically, the BCOP/CoFe2O4/MIL-53(Al) sample exhibited a specific surface area of 196.430 m2/g and a magnetic saturation value of 9.704 emu/g. The maximum FL ion adsorption capacities for BCOP, BCOP/CoFe2O4, and BCOP/CoFe2O4/MIL-53(Al) were 7.618, 16.330, and 37.320 mg/g, respectively, indicating that the modifications significantly enhanced the adsorption capacity. The optimum fluoride ion removal rates using BCOP, BCOP/CoFe2O4, and BCOP/CoFe2O4/MIL-53(Al) were 97.88%, 98.23%, and 99.06%, respectively, at adsorbent doses of 2.5, 1.5, and 0.8 g/L, contact times of 90, 70, and 50 min, pH 4, temperature 50 °C, and a FL concentration of 10 mg/L. Thermodynamic studies revealed that the adsorption process was spontaneous and endothermic, with increased randomness between the adsorbent and fluoride ions. Kinetic analyses showed that fluoride ion adsorption by BCOP/CoFe2O4/MIL-53(Al) followed a pseudo-second-order (PSO) model, while BCOP and BCOP/CoFe2O4 followed a pseudo-first-order (PFO) model. Additionally, the equilibrium data for fluoride ion adsorption on BCOP/CoFe2O4/MIL-53(Al) adhered to the Freundlich model, whereas the other samples conformed to the Langmuir model. The study evaluates the effectiveness of BCOP, BCOP/CoFe2O4, and BCOP/CoFe2O4/MIL-53(Al) in removing FL ions from glass manufacturing wastewater, highlighting the superior performance of the magnetic composite due to its enhanced surface area and functional groups. Notably, the adsorbents demonstrated good regenerative capabilities, maintaining high performance over multiple adsorption cycles.

Defect-Engineered MOF-801/Sodium Alginate Aerogel Beads for Boosting Adsorption of Pb(II)

Metal-organic frameworks (MOFs) are attractive adsorbents for heavy metal capture due to their superior stability, easy modification, and adjustable pore size. However, their inherent microporous structure poses challenges in achieving a higher adsorption capacity. Defect engineering is considered a simple method to create hierarchical MOFs with larger pores. Here, we employed l-aspartic acid as a mixed linker to bind Zr4+ clusters in competition with fumaric acid of MOF-801 to create defects, and the pore size was increased from 4.66 to 15.65 nm. Mercaptosuccinic acid was subsequently used as a postexchange ligand to graft the resultant MOF-801 by acid-ammonia condensation to further expand the pore size to 22.73 nm. Notably, the -NH2, -COOH, and -SH groups contributed by these two ligands increased the adsorption sites for Pb(II). The obtained defective MOF-801 with larger pores was thereafter loaded onto sodium alginate to form aerogel beads as adsorbents, and an adsorption capacity of 375.48 mg/g for Pb(II) was achieved, which is ∼51 times that of pristine MOF-801. The aerogel beads also exhibited outstanding reusability with a removal efficiency of ∼90.23% after 5 cycles of use. The adsorption mechanism of Pb(II) included ion-exchange interaction, as well as chelation interactions of Pb-O, Pb-NH2, and Pb-S. The versatile combination of defect engineering and composite beads provides novel inspirations for MOF modification for boosting heavy metal adsorption.

COF-derived porous nitrogen-doped carbon for removal of emerging organic contaminants and efficient uranium extraction from seawater

The development of adsorbents for efficient and highly selective seawater extraction of uranium was instrumental in fostering sustainable progress in energy and addressing the prevailing energy crisis. However, the complex background composition of the marine environment, including radionuclides, organic pollutants, and a large number of co-existing heavy metal ions, were non-negligible obstacles to the extraction of uranium from seawater. The present investigation successfully employed a self-templated approach to synthesize porous nitrogen-doped carbon (PNC) derived from COF, which exhibited tremendous potential as an adsorbent for pollutant removal in environmental treatment. LZU1@PNC not only retained the structural features of the original COF-LZU1, but also overcame the acid-base instability problem commonly found in COFs. Subsequently, the removal process of two typical water pollutants on the material was investigated using 2,4-DCP and [UO2(CO3)3]4-. The results demonstrated that LZU1@PNC exhibited superior removal performance for the target pollutants compared to COF-LZU1, owing to its larger specific surface area and abundant defect structure. After six desorption-regeneration cycles, LZU1@PNC still maintained a high removal rate of the target contaminants, demonstrating the stability of this material and its excellent recyclability. In addition, based on various characterization techniques, the removal mechanism of 2,4-DCP was presumed to be mainly electrostatic attraction, hydrogen bonding, and π-π stacking interactions. Conversely, the elimination process of [UO2(CO3)3]4- predominantly relied on surface complexation phenomena. The present investigation provided new perspectives and stimulated a broader study of other COF-derived carbon materials and their modifications as adsorbents for uranium extraction from seawater and other applications.

Yolk-shell MOF-on-MOF hybrid solid-phase microextraction coatings for efficient enrichment and detection of pesticides: Structural regulation cause performance differences

Metal-organic frameworks (MOFs) based composites with different structure-activity relationships have been widely used in the field of organic pollutant adsorption and extraction. Here, two MOF-on-MOF composites with different structures (yolk-shell and core-shell) from homologous sources were prepared by a simple in-situ growth synthesis method and structural regulation. In order to verify the effect of composite structure on the extraction capacity, the adsorption performance of the yolk-shell structure (YS-NH2-UiO-66@CoZn-ZIF) and the core-shell structured (NH2-UiO-66@CoZn-ZIF) material were compared by using them as coating material of direct immersion solid-phase microextraction (DI-SPME) to enrich six pesticides in five matrices. The results showed that because of the unique hollow hierarchical structure, high specific surface area (930.68 m2 g-1), abundant and open active sites, and synergistic and complementary adsorption forces, YS-NH2-UiO-66@CoZn-ZIF composites had the maximum adsorption amount of 36.01-66.31 mg g-1 under the same experiment condition, which was 6.81%-34.26 % higher than that of NH2-UiO-66@CoZn-ZIF. In addition, the adsorption mechanism of the prepared materials was verified and elaborated through theoretical simulations and material characterization. Under the optimized conditions, the YS-NH2-UiO-66@CoZn-ZIF-coated SPME-HPLC-UV method had a wide linear range (0.241-500 μg L-1), a good linear correlation coefficient (R2 > 0.9988), a low detection limits (0.072-0.567 μg L-1, S/N = 3) and low quantification limits (0.241-1.891 μg L-1, S/N = 10). The relative standard deviations of individual fibers and different batches of fibers were 0.47-6.20 % and 0.22-2.48 %, respectively, and individual fibers could be recycled more than 104 times. This work provided a good synthetic route and comparative ideas for exploring the in-situ growth synthesis of yolk-shell composites with reasonable structure-activity relationships.

Unveiling the scope and perspectives of MOF-derived materials for cutting-edge applications

Although synthesis and design of MOFs are crucial factors to the successful implementation of targeted applications, there is still lack of knowledge among researchers about the synthesis of MOFs and their derived composites for practical applications. For example, many researchers manipulate study results, and it has become quite difficult to quit this habit specifically among the young researchers Undoubtedly, MOFs have become an excellent class of compounds but there are many challenges associated with their improvement to attain diverse applications. It has been noted that MOF-derived materials have gained considerable interest owing to their unique chemical properties. These compounds have exhibited excellent potential in various sectors such as energy, catalysis, sensing and environmental applications. It is worth mentioning that most of the researchers rely on commercially available MOFs for use as precursor supports, but it is an unethical and wrong practice because it prevents the exploration of the hidden diversity of similar materials. The reported studies have significant gaps and flaws, they do not have enough details about the exact parameters used for the synthesis of MOFs and their derived materials. For example, many young researchers claim that MOF-based materials cannot be synthesized as per the reported instructions for large-scale implementation. In this regard, current article provides a comprehensive review of the most recent advancements in the design of MOF-derived materials. The methodologies and applications have been evaluated together with their advantages and drawbacks. Additionally, this review suggests important precautions and solutions to overcome the drawbacks associated with their preparation. Applications of MOF-derived materials in the fields of energy, catalysis, sensing and environment have been discussed. No doubt, these materials have become excellent class but there are still many challenges ahead to specify it for the targeted applications.

Enhanced fluoride removal using montmorillonite clay modified with CoFe2O4 and metal-organic frameworks

The use of modified clays can play an effective role as an effective adsorbent in removing fluoride (Flu) ions from water and aqueous solutions. In the present research, montmorillonite clay (MMt) was modified using CoFe2O4 magnetic particles and Al-Fe fumarate metal-organic framework (Al-Fe Fum) and was utilized as an efficient adsorbent for removing Flu from aqueous solution. The properties of MMt and MMt/CoFe2O4/Al-Fe Fum samples were investigated using different techniques. The results showed that with the modification of MMt using CoFe2O4 magnetic particles and the metal-organic framework of Al-Fe Fum, the BET surface has increased notably from 13.217 to 365.80 m2/g. To investigate the effect of independent variables and their interaction on the efficiency of the Flu adsorption, response surface method-central compound design (RSM-CCD) was served. Based on the results of ANOVA, the F-value and p-value parameters for the desired model were determined to be 783.09 and < 0.0001, respectively, which confirms the success and high ability of the model. The number of R2, adjusted R2, and Predicted R2 for adsorption of Flu ion was determined to be 0.998, 0.997, and 0.995, respectively, which shows that the proposed regression model can describe the process of adsorption and interaction between variables well. Compared to other kinetic models, the pseudo 2nd order kinetic model has a greater ability to describe the Flu adsorption behavior. The R2 parameter value determined that the Freundlich isotherm model has a suitable ability to investigate the isotherm behavior and confirms the effect of heterogeneous surfaces in the process. Generally, the outcomes signified that the MMt and MMt/CoFe2O4/Al-Fe Fum samples can be reused several times in the process of Flu adsorption, while the efficiency is more than 90%.

La-Ce-MOF nanocomposite coated quartz crystal microbalance gas sensor for the detection of amine gases and formaldehyde

Trimethylamine (TMA), Dimethylamine (DMA), Ammonia (NH3) and formaldehyde (HCHO) are typical volatile gases and able to cause great damage to the environment and the human body, and they may appear along in some particular cases such as marine meat spoilage. However, gas sensors can detect all the 4 hazardous gases simultaneously have rarely been reported. In this study, a quartz crystal microbalance (QCM) gas sensor modified with La-Ce-MOF was employed for the detection of 4 target gases (TMA, DMA, NH3 and HCHO). The sensor exhibited excellent stability (63 days), selectivity (3.51 Hz/(μmoL/L) for TMA, 4.19 Hz/(μmoL/L) for DMA, 3.14·Hz/(μmoL/L) for NH3 and 3.08·Hz/(μmoL/L) for HCHO), robustness and sensitivity towards target gases detection. Vienna Ab-initio Simulation Package calculations showed that this superior sensing performance was attributed to the preferential adsorption of target gas molecules onto the nanomicrospheres via hydrogen bond. The adsorption energy was - 0.4329 eV for TMA, - 0.5204 eV for DMA, - 0.6823 eV for NH3 and - 0.7576 eV for HCHO, all of which are physically adsorbed. In the detection of hazardous gases, sensor surface active sites were often susceptible to environmental factors and interfering substances, leading to a decrease in the sensitivity of the gas sensor, which in turn affects the signal accuracy in practical applications. This issue has been effectively addressed and the sensor has been implemented for the assessment of the salmon meat freshness, which may contribute to further advancements in the development of QCM gas sensors for monitoring food quality, human beings health and environment safety.